MRI RF catheter coil

Abstract

A radio frequency coil ( 12, 19 ) adapted for use in interventional magnetic resonance imaging consists of a loop of an elongated electric conductor arranged to form a twisted wire pair ( 12, 19 ) and means associated with it for operating the coil both in transmit and receive mode, in order that the coil does not image anything but tracks its own path on an MR image, without affecting the magnetization in the main bulk of the body being imaged.

What is claimed is:  
     
       1. A radio frequency coil adapter for use in interventional magnetic resonance imaging, the coil comprising: 
       a loop of an elongated electric conductor having outward and return portions arranged to form a twisted pair; and  
       means for operating the coil in both transmit and receive modes,  
       wherein, when in the receive mode, said coil has a net sensitivity to nuclear magnetic resonance signals only from tissue substantially adjacent thereto, and, when in the transmit mode, said coil excites only tissue substantially adjacent thereto without substantially affecting bulk tissue magnetization.  
     
     
       2. The coil of claim  1  wherein the outward and return sections are insulated. 
     
     
       3. The coil of claim  1  wherein the overall width of the coil is less than 1.5 mm and a pitch of the twisted pair is approximately 6.5 mm. 
     
     
       4. The coil of claim  1  wherein the coil is inductively coupled to the processing electronics of a magnetic resonance imaging apparatus. 
     
     
       5. The coil of claim  1  wherein the means for operating comprise a transmit/receive switch and an r.f. amplifier. 
     
     
       6. The coil of claim  1  wherein the coil is inserted in a catheter. 
     
     
       7. The coil of claim  1  wherein the coil is adapted for use as a catheter guidewire. 
     
     
       8. The coil of claim  1  wherein the coil is affixed to a surgical instrument. 
     
     
       9. The coil of claim  8  wherein the surgical instrument is a catheter and the coil is built into the wall of the catheter. 
     
     
       10. A method of interventional magnetic resonance imaging, the method comprising the steps of: 
       inserting a patient to be imaged in an imaging region of a magnetic resonance imaging apparatus;  
       placing a coil within the patient, said coil being substantially decoupled from a transmit coil and said coil comprising a loop of elongated electrical conductor, the conductor having outward and return portions arranged to form a twisted pair; and,  
       operating the coil as a transmitter and as a receiver during respective portions of a magnetic resonance excitation and detection sequence so as to obtain an indication of a position of the coil in relation to surrounding anatomy of the patient.  
     
     
       11. The method of claim  10  wherein the coil is operated as a transmitter during a B 1  r.f. excitation pulse generated during the sequence. 
     
     
       12. The method of claim  10  further comprising the steps of: 
       inserting a catheter within the patient to be imaged; and  
       inserting the loop within the catheter.  
     
     
       13. The method of claim  10  further comprising the step of using the coil to guide the application of a medical instrument. 
     
     
       14. The method of claim  13  wherein the medical instrument is a catheter. 
     
     
       15. The method according to claim  13  further comprising the step of removing the coil from the patient. 
     
     
       16. A method of magnetic resonance imaging comprising the steps of: 
       (a) applying an r.f. pulse sequence and gradient pulse sequence in the presence of a main magnetic field in order to produce an MR image of a patient;  
       (b) inserting a coil within the anatomy of the patient, the coil comprising an electrical conductor wound in a bifilar configuration;  
       (c) applying an r.f. transmission pulse sequence to the coil and detecting resulting relaxation signals with the coil in order to produce an image of the coils's path; and,  
       (d) superimposing the image of the coil's path on the MR image of the patient so as to obtain an indication of the location of the coil in relation to the anatomy of the patient.  
     
     
       17. The method of claim  16  further comprising the step of using the coil as a guidewire. 
     
     
       18. The method of claim  16  wherein the position of the coil with respect to a surgical instrument is known and further comprising the step of using the position of the coil to provide and indication of the position of the instrument. 
     
     
       19. The method of claim  17  wherein the instrument is a catheter and the coil is affixed to the catheter. 
     
     
       20. The method of claim  17  wherein the instrument is a catheter and the coil is located within the catheter. 
     
     
       21. The method of claim  16  wherein magnetic gradients used in connection with producing the MR image of the patient are substantially identical to magnetic gradients used in connection with producing the image of the coil's path. 
     
     
       22. The method according to claim  16  further comprising the steps of: 
       (e) carrying out an additional step (b) following step (c) without waiting for a bulk magnetization of the patient to be restored.